The present invention concerns interrupt signals to interrupt execution of an instruction in a computing system when performing calculations on one or more operands.
The term interruption is utilized to discuss the basic mechanism which handles traps, checks, faults and interrupts. Traps include two sorts of possibilities: either the functions or operations requested by a current instruction cannot or should not be carried out, or system intervention is desired by the user before or after the instruction is executed. Examples of the first possibility include arithmetic operations which result in overflow and instructions executed with insufficient privilege for their intended function.
Typically, when an arithmetic operation results in an overflow, the overflow is either ignored or is "trapped" out utilizing a data trap. When the overflow is ignored, meaningless data may result and be used in the execution of the remainder of the instruction. Typically, the processor status word (PSW) contains a bit which directs overflow control. This results in a global instruction for overflow trapping which complicates the operating system design and user application programs. Further, selective trapping of a data overflow is not possible without changing the PSW bit which provides overflow control.